An apparatus for recovering exhaust gas is installed in a large number of converters at present to recover exhaust gas generated from the converter during blowing. Recovered exhaust gas in converter contains a large amount of CO, and therefore the recovered exhaust gas is an important energy source in view of the recent high cost of petroluem. In order to increase the energy level in the exhaust gas to be recovered, the following various methods have hitherto been carried out.
1. The ratio of charge for recovering OG gas is increased.
2. The amount of air sucked into the duct is decreased in order to recover CO, which is generated from converter, without combustion as possible.
3. The time from the beginning of blowing to the beginning of recovering of exhaust gas, and the time from the completion of recovering of exhaust gas to the completion of blowing are made as short as possible. That is, the time for recoving exhaust gas during blowing is made long as possible. For this purpose, for example, analysis of components of exhaust gas is carried out in a shorter period of time.
However, the amount of CO gas generated from converter is limited, and further exhaust gas must be kept to a composition outside of the explosion composition in view of the safety operation. Accordingly, when these conditions are taken into consideration, the above described methods are still insufficient.
There have been proposed ideas, wherein a conventional converter-exhaust gas recovering apparatus is used not only for collecting generated gas, but also for converting the energy system and recovering the converted energy system. As one of these ideas, a method has been proposed, wherein coke or coal as a carbon source is charged into a converter and reacted with O.sub.2 therein so as to be converted into CO gas, and the resulting CO gas is recovered. However, in this method, a large amount of oxygen source must be additionally added in order to convert C into CO, and further the cost of coke or coal must be taken into consideration, and therefore a high merit can not be expected.
While, in the conventional technic, limestone has been used for a long time as a solvent in a converter. Particularly, in an LD converter, limestone has been used as an inexpensive substitute for quicklime, and further as a cooling agent. However, when limestone is charged into a converter from its top, substantially all the limestone is decomposed to form CaO and CO.sub.2 gas through the reaction represented by the following formula (1), and it is impossible to increase the recovered amount of CO-rich exchaust gas. EQU CaCO.sub.3 .fwdarw.CaO+CO.sub.2 . . . ( 1)
Further, quicklime generally used at present in converter is produced according the formula (1) by roasting limestone, and CO.sub.2 generated as a by-product in the reaction is discarded at present.